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TOMOYO Linux Cross Reference
Linux/kernel/stop_machine.c

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  1 /*
  2  * kernel/stop_machine.c
  3  *
  4  * Copyright (C) 2008, 2005     IBM Corporation.
  5  * Copyright (C) 2008, 2005     Rusty Russell rusty@rustcorp.com.au
  6  * Copyright (C) 2010           SUSE Linux Products GmbH
  7  * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
  8  *
  9  * This file is released under the GPLv2 and any later version.
 10  */
 11 #include <linux/completion.h>
 12 #include <linux/cpu.h>
 13 #include <linux/init.h>
 14 #include <linux/kthread.h>
 15 #include <linux/export.h>
 16 #include <linux/percpu.h>
 17 #include <linux/sched.h>
 18 #include <linux/stop_machine.h>
 19 #include <linux/interrupt.h>
 20 #include <linux/kallsyms.h>
 21 #include <linux/smpboot.h>
 22 #include <linux/atomic.h>
 23 #include <linux/nmi.h>
 24 #include <linux/sched/wake_q.h>
 25 
 26 /*
 27  * Structure to determine completion condition and record errors.  May
 28  * be shared by works on different cpus.
 29  */
 30 struct cpu_stop_done {
 31         atomic_t                nr_todo;        /* nr left to execute */
 32         int                     ret;            /* collected return value */
 33         struct completion       completion;     /* fired if nr_todo reaches 0 */
 34 };
 35 
 36 /* the actual stopper, one per every possible cpu, enabled on online cpus */
 37 struct cpu_stopper {
 38         struct task_struct      *thread;
 39 
 40         raw_spinlock_t          lock;
 41         bool                    enabled;        /* is this stopper enabled? */
 42         struct list_head        works;          /* list of pending works */
 43 
 44         struct cpu_stop_work    stop_work;      /* for stop_cpus */
 45 };
 46 
 47 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
 48 static bool stop_machine_initialized = false;
 49 
 50 /* static data for stop_cpus */
 51 static DEFINE_MUTEX(stop_cpus_mutex);
 52 static bool stop_cpus_in_progress;
 53 
 54 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
 55 {
 56         memset(done, 0, sizeof(*done));
 57         atomic_set(&done->nr_todo, nr_todo);
 58         init_completion(&done->completion);
 59 }
 60 
 61 /* signal completion unless @done is NULL */
 62 static void cpu_stop_signal_done(struct cpu_stop_done *done)
 63 {
 64         if (atomic_dec_and_test(&done->nr_todo))
 65                 complete(&done->completion);
 66 }
 67 
 68 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
 69                                         struct cpu_stop_work *work,
 70                                         struct wake_q_head *wakeq)
 71 {
 72         list_add_tail(&work->list, &stopper->works);
 73         wake_q_add(wakeq, stopper->thread);
 74 }
 75 
 76 /* queue @work to @stopper.  if offline, @work is completed immediately */
 77 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 78 {
 79         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 80         DEFINE_WAKE_Q(wakeq);
 81         unsigned long flags;
 82         bool enabled;
 83 
 84         preempt_disable();
 85         raw_spin_lock_irqsave(&stopper->lock, flags);
 86         enabled = stopper->enabled;
 87         if (enabled)
 88                 __cpu_stop_queue_work(stopper, work, &wakeq);
 89         else if (work->done)
 90                 cpu_stop_signal_done(work->done);
 91         raw_spin_unlock_irqrestore(&stopper->lock, flags);
 92 
 93         wake_up_q(&wakeq);
 94         preempt_enable();
 95 
 96         return enabled;
 97 }
 98 
 99 /**
100  * stop_one_cpu - stop a cpu
101  * @cpu: cpu to stop
102  * @fn: function to execute
103  * @arg: argument to @fn
104  *
105  * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
106  * the highest priority preempting any task on the cpu and
107  * monopolizing it.  This function returns after the execution is
108  * complete.
109  *
110  * This function doesn't guarantee @cpu stays online till @fn
111  * completes.  If @cpu goes down in the middle, execution may happen
112  * partially or fully on different cpus.  @fn should either be ready
113  * for that or the caller should ensure that @cpu stays online until
114  * this function completes.
115  *
116  * CONTEXT:
117  * Might sleep.
118  *
119  * RETURNS:
120  * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
121  * otherwise, the return value of @fn.
122  */
123 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
124 {
125         struct cpu_stop_done done;
126         struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
127 
128         cpu_stop_init_done(&done, 1);
129         if (!cpu_stop_queue_work(cpu, &work))
130                 return -ENOENT;
131         /*
132          * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
133          * cycle by doing a preemption:
134          */
135         cond_resched();
136         wait_for_completion(&done.completion);
137         return done.ret;
138 }
139 
140 /* This controls the threads on each CPU. */
141 enum multi_stop_state {
142         /* Dummy starting state for thread. */
143         MULTI_STOP_NONE,
144         /* Awaiting everyone to be scheduled. */
145         MULTI_STOP_PREPARE,
146         /* Disable interrupts. */
147         MULTI_STOP_DISABLE_IRQ,
148         /* Run the function */
149         MULTI_STOP_RUN,
150         /* Exit */
151         MULTI_STOP_EXIT,
152 };
153 
154 struct multi_stop_data {
155         cpu_stop_fn_t           fn;
156         void                    *data;
157         /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
158         unsigned int            num_threads;
159         const struct cpumask    *active_cpus;
160 
161         enum multi_stop_state   state;
162         atomic_t                thread_ack;
163 };
164 
165 static void set_state(struct multi_stop_data *msdata,
166                       enum multi_stop_state newstate)
167 {
168         /* Reset ack counter. */
169         atomic_set(&msdata->thread_ack, msdata->num_threads);
170         smp_wmb();
171         msdata->state = newstate;
172 }
173 
174 /* Last one to ack a state moves to the next state. */
175 static void ack_state(struct multi_stop_data *msdata)
176 {
177         if (atomic_dec_and_test(&msdata->thread_ack))
178                 set_state(msdata, msdata->state + 1);
179 }
180 
181 /* This is the cpu_stop function which stops the CPU. */
182 static int multi_cpu_stop(void *data)
183 {
184         struct multi_stop_data *msdata = data;
185         enum multi_stop_state curstate = MULTI_STOP_NONE;
186         int cpu = smp_processor_id(), err = 0;
187         unsigned long flags;
188         bool is_active;
189 
190         /*
191          * When called from stop_machine_from_inactive_cpu(), irq might
192          * already be disabled.  Save the state and restore it on exit.
193          */
194         local_save_flags(flags);
195 
196         if (!msdata->active_cpus)
197                 is_active = cpu == cpumask_first(cpu_online_mask);
198         else
199                 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
200 
201         /* Simple state machine */
202         do {
203                 /* Chill out and ensure we re-read multi_stop_state. */
204                 cpu_relax_yield();
205                 if (msdata->state != curstate) {
206                         curstate = msdata->state;
207                         switch (curstate) {
208                         case MULTI_STOP_DISABLE_IRQ:
209                                 local_irq_disable();
210                                 hard_irq_disable();
211                                 break;
212                         case MULTI_STOP_RUN:
213                                 if (is_active)
214                                         err = msdata->fn(msdata->data);
215                                 break;
216                         default:
217                                 break;
218                         }
219                         ack_state(msdata);
220                 } else if (curstate > MULTI_STOP_PREPARE) {
221                         /*
222                          * At this stage all other CPUs we depend on must spin
223                          * in the same loop. Any reason for hard-lockup should
224                          * be detected and reported on their side.
225                          */
226                         touch_nmi_watchdog();
227                 }
228         } while (curstate != MULTI_STOP_EXIT);
229 
230         local_irq_restore(flags);
231         return err;
232 }
233 
234 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
235                                     int cpu2, struct cpu_stop_work *work2)
236 {
237         struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
238         struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
239         DEFINE_WAKE_Q(wakeq);
240         int err;
241 
242 retry:
243         /*
244          * The waking up of stopper threads has to happen in the same
245          * scheduling context as the queueing.  Otherwise, there is a
246          * possibility of one of the above stoppers being woken up by another
247          * CPU, and preempting us. This will cause us to not wake up the other
248          * stopper forever.
249          */
250         preempt_disable();
251         raw_spin_lock_irq(&stopper1->lock);
252         raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
253 
254         if (!stopper1->enabled || !stopper2->enabled) {
255                 err = -ENOENT;
256                 goto unlock;
257         }
258 
259         /*
260          * Ensure that if we race with __stop_cpus() the stoppers won't get
261          * queued up in reverse order leading to system deadlock.
262          *
263          * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
264          * queued a work on cpu1 but not on cpu2, we hold both locks.
265          *
266          * It can be falsely true but it is safe to spin until it is cleared,
267          * queue_stop_cpus_work() does everything under preempt_disable().
268          */
269         if (unlikely(stop_cpus_in_progress)) {
270                 err = -EDEADLK;
271                 goto unlock;
272         }
273 
274         err = 0;
275         __cpu_stop_queue_work(stopper1, work1, &wakeq);
276         __cpu_stop_queue_work(stopper2, work2, &wakeq);
277 
278 unlock:
279         raw_spin_unlock(&stopper2->lock);
280         raw_spin_unlock_irq(&stopper1->lock);
281 
282         if (unlikely(err == -EDEADLK)) {
283                 preempt_enable();
284 
285                 while (stop_cpus_in_progress)
286                         cpu_relax();
287 
288                 goto retry;
289         }
290 
291         wake_up_q(&wakeq);
292         preempt_enable();
293 
294         return err;
295 }
296 /**
297  * stop_two_cpus - stops two cpus
298  * @cpu1: the cpu to stop
299  * @cpu2: the other cpu to stop
300  * @fn: function to execute
301  * @arg: argument to @fn
302  *
303  * Stops both the current and specified CPU and runs @fn on one of them.
304  *
305  * returns when both are completed.
306  */
307 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
308 {
309         struct cpu_stop_done done;
310         struct cpu_stop_work work1, work2;
311         struct multi_stop_data msdata;
312 
313         msdata = (struct multi_stop_data){
314                 .fn = fn,
315                 .data = arg,
316                 .num_threads = 2,
317                 .active_cpus = cpumask_of(cpu1),
318         };
319 
320         work1 = work2 = (struct cpu_stop_work){
321                 .fn = multi_cpu_stop,
322                 .arg = &msdata,
323                 .done = &done
324         };
325 
326         cpu_stop_init_done(&done, 2);
327         set_state(&msdata, MULTI_STOP_PREPARE);
328 
329         if (cpu1 > cpu2)
330                 swap(cpu1, cpu2);
331         if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
332                 return -ENOENT;
333 
334         wait_for_completion(&done.completion);
335         return done.ret;
336 }
337 
338 /**
339  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
340  * @cpu: cpu to stop
341  * @fn: function to execute
342  * @arg: argument to @fn
343  * @work_buf: pointer to cpu_stop_work structure
344  *
345  * Similar to stop_one_cpu() but doesn't wait for completion.  The
346  * caller is responsible for ensuring @work_buf is currently unused
347  * and will remain untouched until stopper starts executing @fn.
348  *
349  * CONTEXT:
350  * Don't care.
351  *
352  * RETURNS:
353  * true if cpu_stop_work was queued successfully and @fn will be called,
354  * false otherwise.
355  */
356 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
357                         struct cpu_stop_work *work_buf)
358 {
359         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
360         return cpu_stop_queue_work(cpu, work_buf);
361 }
362 
363 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
364                                  cpu_stop_fn_t fn, void *arg,
365                                  struct cpu_stop_done *done)
366 {
367         struct cpu_stop_work *work;
368         unsigned int cpu;
369         bool queued = false;
370 
371         /*
372          * Disable preemption while queueing to avoid getting
373          * preempted by a stopper which might wait for other stoppers
374          * to enter @fn which can lead to deadlock.
375          */
376         preempt_disable();
377         stop_cpus_in_progress = true;
378         for_each_cpu(cpu, cpumask) {
379                 work = &per_cpu(cpu_stopper.stop_work, cpu);
380                 work->fn = fn;
381                 work->arg = arg;
382                 work->done = done;
383                 if (cpu_stop_queue_work(cpu, work))
384                         queued = true;
385         }
386         stop_cpus_in_progress = false;
387         preempt_enable();
388 
389         return queued;
390 }
391 
392 static int __stop_cpus(const struct cpumask *cpumask,
393                        cpu_stop_fn_t fn, void *arg)
394 {
395         struct cpu_stop_done done;
396 
397         cpu_stop_init_done(&done, cpumask_weight(cpumask));
398         if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
399                 return -ENOENT;
400         wait_for_completion(&done.completion);
401         return done.ret;
402 }
403 
404 /**
405  * stop_cpus - stop multiple cpus
406  * @cpumask: cpus to stop
407  * @fn: function to execute
408  * @arg: argument to @fn
409  *
410  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
411  * @fn is run in a process context with the highest priority
412  * preempting any task on the cpu and monopolizing it.  This function
413  * returns after all executions are complete.
414  *
415  * This function doesn't guarantee the cpus in @cpumask stay online
416  * till @fn completes.  If some cpus go down in the middle, execution
417  * on the cpu may happen partially or fully on different cpus.  @fn
418  * should either be ready for that or the caller should ensure that
419  * the cpus stay online until this function completes.
420  *
421  * All stop_cpus() calls are serialized making it safe for @fn to wait
422  * for all cpus to start executing it.
423  *
424  * CONTEXT:
425  * Might sleep.
426  *
427  * RETURNS:
428  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
429  * @cpumask were offline; otherwise, 0 if all executions of @fn
430  * returned 0, any non zero return value if any returned non zero.
431  */
432 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
433 {
434         int ret;
435 
436         /* static works are used, process one request at a time */
437         mutex_lock(&stop_cpus_mutex);
438         ret = __stop_cpus(cpumask, fn, arg);
439         mutex_unlock(&stop_cpus_mutex);
440         return ret;
441 }
442 
443 /**
444  * try_stop_cpus - try to stop multiple cpus
445  * @cpumask: cpus to stop
446  * @fn: function to execute
447  * @arg: argument to @fn
448  *
449  * Identical to stop_cpus() except that it fails with -EAGAIN if
450  * someone else is already using the facility.
451  *
452  * CONTEXT:
453  * Might sleep.
454  *
455  * RETURNS:
456  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
457  * @fn(@arg) was not executed at all because all cpus in @cpumask were
458  * offline; otherwise, 0 if all executions of @fn returned 0, any non
459  * zero return value if any returned non zero.
460  */
461 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
462 {
463         int ret;
464 
465         /* static works are used, process one request at a time */
466         if (!mutex_trylock(&stop_cpus_mutex))
467                 return -EAGAIN;
468         ret = __stop_cpus(cpumask, fn, arg);
469         mutex_unlock(&stop_cpus_mutex);
470         return ret;
471 }
472 
473 static int cpu_stop_should_run(unsigned int cpu)
474 {
475         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
476         unsigned long flags;
477         int run;
478 
479         raw_spin_lock_irqsave(&stopper->lock, flags);
480         run = !list_empty(&stopper->works);
481         raw_spin_unlock_irqrestore(&stopper->lock, flags);
482         return run;
483 }
484 
485 static void cpu_stopper_thread(unsigned int cpu)
486 {
487         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
488         struct cpu_stop_work *work;
489 
490 repeat:
491         work = NULL;
492         raw_spin_lock_irq(&stopper->lock);
493         if (!list_empty(&stopper->works)) {
494                 work = list_first_entry(&stopper->works,
495                                         struct cpu_stop_work, list);
496                 list_del_init(&work->list);
497         }
498         raw_spin_unlock_irq(&stopper->lock);
499 
500         if (work) {
501                 cpu_stop_fn_t fn = work->fn;
502                 void *arg = work->arg;
503                 struct cpu_stop_done *done = work->done;
504                 int ret;
505 
506                 /* cpu stop callbacks must not sleep, make in_atomic() == T */
507                 preempt_count_inc();
508                 ret = fn(arg);
509                 if (done) {
510                         if (ret)
511                                 done->ret = ret;
512                         cpu_stop_signal_done(done);
513                 }
514                 preempt_count_dec();
515                 WARN_ONCE(preempt_count(),
516                           "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
517                 goto repeat;
518         }
519 }
520 
521 void stop_machine_park(int cpu)
522 {
523         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
524         /*
525          * Lockless. cpu_stopper_thread() will take stopper->lock and flush
526          * the pending works before it parks, until then it is fine to queue
527          * the new works.
528          */
529         stopper->enabled = false;
530         kthread_park(stopper->thread);
531 }
532 
533 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
534 
535 static void cpu_stop_create(unsigned int cpu)
536 {
537         sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
538 }
539 
540 static void cpu_stop_park(unsigned int cpu)
541 {
542         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
543 
544         WARN_ON(!list_empty(&stopper->works));
545 }
546 
547 void stop_machine_unpark(int cpu)
548 {
549         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
550 
551         stopper->enabled = true;
552         kthread_unpark(stopper->thread);
553 }
554 
555 static struct smp_hotplug_thread cpu_stop_threads = {
556         .store                  = &cpu_stopper.thread,
557         .thread_should_run      = cpu_stop_should_run,
558         .thread_fn              = cpu_stopper_thread,
559         .thread_comm            = "migration/%u",
560         .create                 = cpu_stop_create,
561         .park                   = cpu_stop_park,
562         .selfparking            = true,
563 };
564 
565 static int __init cpu_stop_init(void)
566 {
567         unsigned int cpu;
568 
569         for_each_possible_cpu(cpu) {
570                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
571 
572                 raw_spin_lock_init(&stopper->lock);
573                 INIT_LIST_HEAD(&stopper->works);
574         }
575 
576         BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
577         stop_machine_unpark(raw_smp_processor_id());
578         stop_machine_initialized = true;
579         return 0;
580 }
581 early_initcall(cpu_stop_init);
582 
583 int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
584                             const struct cpumask *cpus)
585 {
586         struct multi_stop_data msdata = {
587                 .fn = fn,
588                 .data = data,
589                 .num_threads = num_online_cpus(),
590                 .active_cpus = cpus,
591         };
592 
593         lockdep_assert_cpus_held();
594 
595         if (!stop_machine_initialized) {
596                 /*
597                  * Handle the case where stop_machine() is called
598                  * early in boot before stop_machine() has been
599                  * initialized.
600                  */
601                 unsigned long flags;
602                 int ret;
603 
604                 WARN_ON_ONCE(msdata.num_threads != 1);
605 
606                 local_irq_save(flags);
607                 hard_irq_disable();
608                 ret = (*fn)(data);
609                 local_irq_restore(flags);
610 
611                 return ret;
612         }
613 
614         /* Set the initial state and stop all online cpus. */
615         set_state(&msdata, MULTI_STOP_PREPARE);
616         return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
617 }
618 
619 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
620 {
621         int ret;
622 
623         /* No CPUs can come up or down during this. */
624         cpus_read_lock();
625         ret = stop_machine_cpuslocked(fn, data, cpus);
626         cpus_read_unlock();
627         return ret;
628 }
629 EXPORT_SYMBOL_GPL(stop_machine);
630 
631 /**
632  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
633  * @fn: the function to run
634  * @data: the data ptr for the @fn()
635  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
636  *
637  * This is identical to stop_machine() but can be called from a CPU which
638  * is not active.  The local CPU is in the process of hotplug (so no other
639  * CPU hotplug can start) and not marked active and doesn't have enough
640  * context to sleep.
641  *
642  * This function provides stop_machine() functionality for such state by
643  * using busy-wait for synchronization and executing @fn directly for local
644  * CPU.
645  *
646  * CONTEXT:
647  * Local CPU is inactive.  Temporarily stops all active CPUs.
648  *
649  * RETURNS:
650  * 0 if all executions of @fn returned 0, any non zero return value if any
651  * returned non zero.
652  */
653 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
654                                   const struct cpumask *cpus)
655 {
656         struct multi_stop_data msdata = { .fn = fn, .data = data,
657                                             .active_cpus = cpus };
658         struct cpu_stop_done done;
659         int ret;
660 
661         /* Local CPU must be inactive and CPU hotplug in progress. */
662         BUG_ON(cpu_active(raw_smp_processor_id()));
663         msdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
664 
665         /* No proper task established and can't sleep - busy wait for lock. */
666         while (!mutex_trylock(&stop_cpus_mutex))
667                 cpu_relax();
668 
669         /* Schedule work on other CPUs and execute directly for local CPU */
670         set_state(&msdata, MULTI_STOP_PREPARE);
671         cpu_stop_init_done(&done, num_active_cpus());
672         queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
673                              &done);
674         ret = multi_cpu_stop(&msdata);
675 
676         /* Busy wait for completion. */
677         while (!completion_done(&done.completion))
678                 cpu_relax();
679 
680         mutex_unlock(&stop_cpus_mutex);
681         return ret ?: done.ret;
682 }
683 

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